HR: 09:05h
AN: U51B-05    [Abstracts]
TI: Numerical models of stress and strain distribution at a Chilean-type subduction zone
AU: * Gerbault, M
EM: gerbault@lmtg.obs-mip.fr
AF: IRD, Univ. Chile, Dpto Geologia, Plaza Ercilla 803, Santiago, Chile
AU: Dorbath, C
EM: catherine.dorbath@eost.u-strasbg.fr
AF: IRD, EOST, 5 rue Rene Descartes, Strasbourg, 67084, France
AB: The Chilean subduction margin presents a large-scale constancy as it spreads along 3000 km from north to south, linked to large scale relatively constant conditions between the subducting Nazca plate and the south american continent. In greater detail, the variable height and width of the Andean mountains or the existance of a Central Depression in the fore-arc indicate the role of rheological differences at depth. A 2D numerical approach calculates the distribution of the stress field and deformation in a model 2000 km wide per 200km deep, in which a basal traction is applied to a flexed oceanic lithosphere, simulating slab-pull over a time-span of 2 Myrs. The influence of the strength of the subduction channel and that of the overriding continent are tested, with the use of elastic-viscous-brittle temperature dependent rheology. Loading of the model is accompanied by the development of localised shear strain from the subduction zone through the continent up to the free surface. A strong subduction interface and a strong continental crust favor the development of a subsiding depression in the forearc, as the crust is dragged downwards coupled to the descending plate. Such a scenario could be valid for the Atacama basin (24°S). The role of the continental mantle is discussed, since high friction along a subduction channel suggests resistant normal forces acting from the continental side at depths corresponding to recorded earthquakes. When such a strong continental mantle wedge is accounted for, it can act as an indenter to the subducting plate, making it deviate and flatten. Finally the models illustrate how potential fluids may use channels of localised shear in the continental mantle to migrate upwards.
DE: 1744 Tectonophysics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8020 Mechanics, theory, and modeling
DE: 8104 Continental margins: convergent
SC: Union [U]
MN: 2007 Joint Assembly